This invention relates to an inkjet printing method using an inkjet recording element containing encapsulated particles.
In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
It is well known that in order to achieve and maintain photographic-quality images on such an image-recording element, an ink jet recording element must:
Be readily wetted so there is no puddling, i.e., coalescence of adjacent ink dots, which leads to non-uniform density
Exhibit no image bleeding
Exhibit the ability to absorb high concentrations of ink and dry quickly to avoid elements blocking together when stacked against subsequent prints or other surfaces
Exhibit no discontinuities or defects due to interactions between the support and/or layer(s), such as cracking, repellencies, comb lines and the like
Not allow unabsorbed dyes to aggregate at the free surface causing dye crystallization, which results in bloom or bronzing effects in the imaged areas
Have an optimized image fastness to avoid fade from contact with water or radiation by daylight, tungsten light, or fluorescent light
An ink jet recording element that simultaneously provides an almost instantaneous ink dry time and good image quality is desirable. However, given the wide range of ink compositions and ink volumes that a recording element needs to accommodate, these requirements of inkjet recording media are difficult to achieve simultaneously.
Inkjet recording elements are known that employ porous or non-porous single layer or multilayer coatings that act as suitable image receiving layers on one or both sides of a porous or non-porous support. Recording elements that use non-porous coatings typically have good image quality but exhibit poor ink dry time. Recording elements that use porous coatings typically contain colloidal particulates and have poorer image quality but exhibit superior dry times.
While a wide variety of different types of porous image-recording elements for use with ink jet printing are known, there are many unsolved problems in the art and many deficiencies in the known products which have severely limited their commercial usefulness. A major challenge in the design of a porous image-recording layer is to be able to obtain good quality, crack-free coatings with as little non-particulate matter as possible. If too much non-particulate matter is present, the image-recording layer will not be porous and will exhibit poor ink dry times.
EPA 813,978 A1 relates to an ink jet recording element wherein an ink absorption layer is used comprising fine particles, a hydrophilic binder and oil drops. However, there is a problem with this element in that the oil drops will migrate to the surface and cause changes in the appearance of the image.
U.S. Pat. No. 6,197,381 B1 relates to the production of a recording sheet from a coating composition comprising fine inorganic particles, a hydrophilic binder and a hydrophobic latex having a glass transition temperature of not more than 30xc2x0 C. However, there is a problem with this recording sheet in that it exhibits poor ink dry times.
Final Program and Proceedings of ISandT NIP14, pp. 150-152, relates to microporous paper having an image-receiving layer comprising inorganic core/organic shell particles. The organic shells are cationic polymers. However, there is no reference to the properties or identities of the cationic polymers.
It is an object of this invention to provide an ink jet printing method employing a porous ink jet recording element that has instant dry time. It is another object of this invention to provide an ink jet printing method employing a porous recording element that has good coating quality, especially reduced cracking. It is another object of this invention to provide an ink jet printing method employing an ink jet recording element that exhibits good image quality.
These and other objects are achieved in accordance with the invention which comprises an inkjet printing method comprising the steps of:
I) providing an ink jet printer that is responsive to digital data signals;
II) loading the printer with a porous ink jet recording element comprising a substrate having thereon a porous image-receiving layer comprising
a) inorganic particles encapsulated with an organic polymer having a Tg of less than about 100xc2x0 C.; and
b) particles having a mean particle size of up to about 5 xcexcm;
III) loading the printer with an ink jet ink composition; and
IV) printing on the image-receiving layer using the ink jet ink composition in response to the digital data signals.
The ink jet recording element employed in the process of the invention has good coating and image quality.
Any inorganic particle may be used to prepare the (a) encapsulated particles employed in the invention, such as metal oxides, hydrated metal oxides, boehmite, clay, calcined clay, calcium carbonate, aluminosilicates, zeolites or barium sulfate. In a preferred embodiment of the invention, the inorganic particles are metal oxides such as silica, available commercially as Nalco(copyright) (Nalco Co.), Ludox(copyright) (DuPont Corp), Snowtex(copyright) (Nissan Chemical Co.), alumina, zirconia or titania. In another preferred embodiment of the invention, the particle size of the inorganic particles is from about 5 nm to about 1000 nm.
The (a) encapsulated particles used in the invention may be prepared in a preferred embodiment by silane coupling chemistry wherein first the surface of the inorganic particles is modified with a silane-containing material, and then one or more monomers is polymerized in the presence of the modified particles. Useful polymerization techniques can be found in xe2x80x9cEmulsion Polymerization and Emulsion Polymersxe2x80x9d, edited by P. A. Lovell and M. S. El-Aassar, John Wiley and Sons, 1997.
Silane coupling agents useful for the modification of inorganic particles as described above include 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyldiethoxymethylsilane, 3-aminopropyldimethoxymethylsilane, 3-aminopropylethoxydimethylsilane, 3-aminopropylmethoxydimethylsilane, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyl dimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, 4-aminobutyltriethoxysilane, 4-aminobutyltrimethoxysilane, N-(2-aminoethyl)-3-aminoisobutylmethyl-dimethoxysilane, and other silane coupler agents listed in Gelest catalogue, pp. 105-259(1997). Most preferred silane coupling agents for the modification of inorganic colloids used in the invention include 3-aminopropyl-triethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyl-diethoxymethylsilane, 3-aminopropyldimethoxymethylsilane, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane.
Another embodiment of the invention relates to preparing the (a) encapsulated particles by polymerizing one or more monomers in the presence of the inorganic particles, without first modifying the surface. Another embodiment relates to preparing these encapsulated particles by adsorbing polymer onto the surface of the inorganic particles. Another embodiment relates to preparing these encapsulated particles by forming chemical bonds between the inorganic particles and the polymer either before or after it is formed from the monomer.
The organic polymer used for encapsulation of the inorganic particles employed in the invention has a Tg of less than about 100xc2x0 C., preferably from about xe2x88x9250xc2x0 C. to about 65xc2x0 C. Methods for determining Tg values of the organic polymers are described in xe2x80x9cIntroduction to Physical Polymer Sciencexe2x80x9d, 2nd Edition by L. H. Sperling, published by John Wiley and Sons, Inc., 1992. For each of the organic polymers in Table 1 below, the Tg value was calculated as the weighted sum of the Tg values for homopolymers derived from each of the individual monomers, i, that make up the polymer:       T    ⁢          xe2x80x83        ⁢    g    =            ∑      i        ⁢                  W        i            ⁢              X        i            
where W is the weight percent of monomer i in the organic polymer, and X is the Tg value for the homopolymer derived from monomer i. Tg values for the homopolymers were taken from xe2x80x9cPolymer Handbookxe2x80x9d, 2nd Edition by J. Brandrup and E. H. Immergut, Editors, published by John Wiley and Sons, Inc., 1975.
In a preferred embodiment of the invention, monomers used to prepare the organic polymers of the (a) encapsulated particles include acrylate and styrene monomers which may have a cationic, anionic, or nonionic functionality such as quaternary ammonium, pyridinium, imidazolium, sulfonate, carboxylate or phosphonate groups. Examples of useful monomers include: n-butyl acrylate, n-ethylacrylate, 2-ethylhexylacrylate, methoxyethylacrylate, methoxyethoxy-ethylacrylate, ethoxyethylacrylate, ethoxyethoxyethylacrylate, 2-ethylhexyl-methacrylate, n-propylacrylate, hydroxyethylacrylate, etc. and cationic monomers such as a salt of trimethylammoniumethyl acrylate and trimethylammoniumethyl methacrylate, a salt of triethylammoniumethyl acrylate and triethylammonium-ethyl methacrylate, a salt of dimethylbenzyl-ammoniumethyl acrylate and dimethylbenzylammoniumethyl methacrylate, a salt of dimethylbutylammonium-ethyl acrylate and dimethylbutylammoniumethyl methacrylate, a salt of dimethylhexylammoniumethyl acrylate and dimethylhexylammoniumethyl methacrylate, a salt of dimethyloctyl-ammoniumethyl acrylate and dimethyloctyl-ammoniumethyl methacrylate, a salt of dimethyldodeceylammoniumethyl acrylate and dimethyldocecyl-ammoniumethyl methacrylate, a salt of dimethyloctadecyl-ammoniumethyl acrylate and dimethyloctadecylammoniumethyl methacrylate, etc. Salts of these cationic monomers which can be used include chloride, bromide, methylsulfate, triflate, etc.
Examples of the organic polymers which can be used in the invention to prepare the a) encapsulated particles include poly(n-butylacrylate-co-vinylbenzyltrimethylammonium chloride), poly(n-butylacrylate-co-vinylbenzyltrimethylammonium bromide), poly(n-butylacrylate-co-vinylbenzyldimethylbenzylammonium chloride) and poly(n-butylacrylate-co-vinylbenzyldimethyloctadecylammonium chloride). In a preferred embodiment of the invention, the polymer can be poly(n-butyl acrylate), poly(2-ethylhexyl acrylate), poly(methoxyethylacrylate), poly(ethoxy-ethylacrylate), poly(n-butylacrylate-co-trimethylammoniumethyl acrylate methylsulfate), poly(n-butylacrylate-co-trimethylammoniumethyl methacrylate methylsulfate) or poly(n-butylacrylate-co-vinylbenzyltrimethylammonium chloride).
Any weight ratio of inorganic particle to organic polymer in the a) encapsulated particles may be used. In a preferred embodiment, the weight ratio is 0.2:1 to 20:1. In another preferred embodiment, the weight ratio is 1:1 to 10:1.
Following are examples of inorganic particles encapsulated with an organic polymer which can be used in the invention:
In a preferred embodiment of the invention, (b) particles which may be used include metal oxides or hydroxides, such as alumina, boehmite, hydrated aluminum oxide, titanium oxide or zirconium oxide; clay; calcium carbonate; calcined clay; inorganic silicates; barium sulfate; or organic particles such as polymeric beads. Examples of organic particles useful in the invention are disclosed and claimed in U.S. patent application Ser. Nos.: 09/458,401, filed Dec. 10, 1999; 09/608,969, filed Jun. 30, 2000; 09/607,417, filed Jun. 30, 2000; 09/608,466 filed Jun. 30, 2000; 09/607,419, filed Jun. 30, 2000; and 09/822,731, filed Mar. 30, 2001; the disclosures of which are hereby incorporated by reference. In still yet another preferred embodiment, the mean particle size of the (b) particles is up to about 5 xcexcm.
In a preferred embodiment of the invention, the (a) encapsulated inorganic particles comprise up to about 50 wt. % of the image-receiving layer. In another preferred embodiment of the invention, the (b) particles comprise at least about 50 wt. % of the image receiving layer.
The image-receiving layer employed in the invention may also contain a polymeric binder in an amount insufficient to alter its porosity. In a preferred embodiment, the polymeric binder is a hydrophilic polymer, such as poly(vinyl alcohol), poly(vinyl pyrrolidone), gelatin, cellulose ethers, poly(oxazolines), poly(vinylacetamides), partially hydrolyzed poly(vinyl acetate/vinyl alcohol), poly(acrylic acid), poly(acrylamide), poly(alkylene oxide), sulfonated or phosphated polyesters and polystyrenes, casein, zein, albumin, chitin, chitosan, dextran, pectin, collagen derivatives, collodian, agarxe2x80x94agar, arrowroot, guar, carrageenan, tragacanth, xanthan, rhamsan and the like; or a low Tg latex such as poly(styrene-co-butadiene), a polyurethane latex, a polyester latex, poly(n-butyl acrylate), poly(n-butyl methacrylate), poly(2-ethylhexyl acrylate), a copolymer of n-butylacrylate and ethylacrylate, a copolymer of vinylacetate and n-butylacrylate, etc. The polymeric binder should be chosen so that it is compatible with the aforementioned particles.
The amount of binder used should be sufficient to impart cohesive strength to the ink jet recording element, but should also be minimized so that the interconnected pore structure formed by the aggregates is not filled in by the binder. In a preferred embodiment of the invention, the weight ratio of the binder to the total amount of particles is from about 1:20 to about 1:5.
In addition to the image-receiving layer, the recording element may also contain a base layer, next to the support, the function of which is to absorb the solvent from the ink. Materials useful for this layer include inorganic particles and polymeric binder.
In addition to the image-receiving layer, the recording element may also contain a layer on top of the image-receiving layer, the function of which is to provide gloss. Materials useful for this layer include sub-micron inorganic particles and/or polymeric binder.
The support for the inkjet recording element used in the invention can be any of those usually used for inkjet receivers, such as resin-coated paper, paper, polyesters, or microporous materials such as polyethylene polymer-containing material sold by PPG Industries, Inc., Pittsburgh, Pa. under the trade name of Teslin(copyright), Tyvek(copyright) synthetic paper (DuPont Corp.), impregnated paper such as Duraform(copyright), and OPPalyte(copyright) films (Mobil Chemical Co.) and other composite films listed in U.S. Pat. No. 5,244,861. Opaque supports include plain paper, coated paper, synthetic paper, photographic paper support, melt-extrusion-coated paper, and laminated paper, such as biaxially oriented support laminates. Biaxially oriented support laminates are described in U.S. Pat. Nos. 5,853,965; 5,866,282; 5,874,205; 5,888,643; 5,888,681; 5,888,683; and 5,888,714, the disclosures of which are hereby incorporated by reference. These biaxially oriented supports include a paper base and a biaxially oriented polyolefin sheet, typically polypropylene, laminated to one or both sides of the paper base. Transparent supports include glass, cellulose derivatives, e.g., a cellulose ester, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate; polyesters, such as poly(ethylene terephthalate), poly(ethylene naphthalate), poly(1,4-cyclohexanedimethylene terephthalate), poly(butylene terephthalate), and copolymers thereof; polyimides; polyamides; polycarbonates; polystyrene; polyolefins, such as polyethylene or polypropylene; polysulfones; polyacrylates; polyetherimides; and mixtures thereof. The papers listed above include a broad range of papers, from high end papers, such as photographic paper to low end papers, such as newsprint. In a preferred embodiment, Ektacolor paper made by Eastman Kodak Co. is employed.
The support used in the invention may have a thickness of from about 50 to about 500 xcexcm, preferably from about 75 to 300 xcexcm. Antioxidants, antistatic agents, plasticizers and other known additives may be incorporated into the support, if desired.
In order to improve the adhesion of the image-receiving layer to the support, the surface of the support may be subjected to a corona-discharge treatment prior to applying the image-receiving layer. The adhesion of the image-receiving layer to the support may also be improved by coating a subbing layer on the support. Examples of materials useful in a subbing layer include halogenated phenols and partially hydrolyzed vinyl chloride-co-vinylacetate polymer.
The coating composition can be coated either from water or organic solvents, however water is preferred. The total solids content should be selected to yield a useful coating thickness in the most economical way, and for particulate coating formulations, solids contents from 10-40 wt. % are typical.
Coating compositions employed in the invention may be applied by any number of well known techniques, including dip-coating, wound-wire rod coating, doctor blade coating, gravure and reverse-roll coating, slide coating, bead coating, extrusion coating, curtain coating and the like. Known coating and drying methods are described in further detail in Research Disclosure no. 308119, published December 1989, pages 1007 to 1008. Slide coating is preferred, in which the base layers and overcoat may be simultaneously applied. After coating, the layers are generally dried by simple evaporation, which may be accelerated by known techniques such as convection heating.
The coating composition may be applied to one or both substrate surfaces through conventional pre-metered or post-metered coating methods such as blade, air knife, rod, roll coating, etc. The choice of coating process would be determined from the economics of the operation and in turn, would determine the formulation specifications such as coating solids, coating viscosity, and coating speed.
The image-receiving layer thickness may range from about 1 to about 60 xcexcm, preferably from about 5 to about 40 xcexcm.
After coating, the ink jet recording element may be subject to calendering or supercalendering to enhance surface smoothness. In a preferred embodiment of the invention, the ink jet recording element is subject to hot soft-nip calendering at a temperature of about 65xc2x0 C. and a pressure of 14000 kg/m at a speed of from about 0.15 m/s to about 0.3 m/s.
In order to impart mechanical durability to an ink jet recording element, crosslinkers which act upon the binder discussed above may be added in small quantities. Such an additive improves the cohesive strength of the layer. Crosslinkers such as carbodiimides, polyfunctional aziridines, aldehydes, isocyanates, epoxides, polyvalent metal cations, and the like may all be used.
To improve colorant fade, UV absorbers, radical quenchers or antioxidants may also be added to the image-receiving layer as is well known in the art. Other additives include pH modifiers, adhesion promoters, rheology modifiers, surfactants, biocides, lubricants, dyes, optical brighteners, matte agents, antistatic agents, etc. In order to obtain adequate coatability, additives known to those familiar with such art such as surfactants, defoamers, alcohol and the like may be used. A common level for coating aids is 0.01 to 0.30 wt. % active coating aid based on the total solution weight. These coating aids can be nonionic, anionic, cationic or amphoteric. Specific examples are described in MCCUTCHEON""s Volume 1: Emulsifiers and Detergents, 1995, North American Edition.
Ink jet inks used to image the recording elements employed in the present invention are well-known in the art. The ink compositions used in inkjet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. The dyes used in such compositions are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, U.S. Pat. Nos. 4,381,946; 4,239,543 and 4,781,758, the disclosures of which are hereby incorporated by reference.
The following examples are provided to illustrate the invention.